This invention relates to circuitry which detects, decodes, and synchronizes incoming data which first identifies the spacecraft for which the data is intended from a set of spacecraft and then provides command data or the like to the identified spacecraft.
There are many applications wherein it is necessary to recognize a predetermined identifying code. Systems requiring recognition of predetermined signal patterns include selective calling communications systems and synchronized data transfer systems. Several pattern recognition techniques are known. One such system is the one disclosed in copending application Ser. No. 89,672 filed Oct. 30, 1979. That system derives a clock pulse whenever a valid data signal is received in mark-and-space format (the absence of marks are considered spaces). Also, that system utilizes a threshold detector which examines a mark-and-space encoded analog waveform which generates two pulse sequences, one corresponding to time periods where the waveform exceeds a positive threshold in a positive fashion and another to those time periods where a negative threshold is exceeded in the negative direction. By measuring the interim of time between each negative threshold pulse and positive threshold pulse, where there is no positive threshold pulse in between, a determination can be made if the original waveform actually transmitted a valid mark waveform. This is a first safeguard to assure that only vaid data is clocked to subsequent data processing equipment. A second safeguard provides for a disection of the coincidence pulse by sampling it at a rate much higher than the frequency of the waveform transmitted. By properly gating the samples, the detected marks and spaces can be used in generating corresponding clocks.